An enhanced adsorption methodology for the detoxification of chromium using n-octylamine impregnated Amberlite XAD-4 polymeric sorbent

Abstract

The remediation of heavy metals requires the development of efficient adsorbents. Macroporous polystyrene divinyl benzene based resins are known for their excellent surface characteristics for the effective adsorption of metals. In this paper, we propose an effective adsorption procedure for chromium (VI) using aliphatic primary amine as a guest in Amberlite XAD-4 polymeric sorbent as the host. The adsorption of chromium was quantitative at pH 2.5. The adsorption process was in accordance with pseudo second order kinetics and the maximum adsorption capacity was found to be 75.93 mg g⁻¹ with good adherence to Langmuir isotherm model. The free energy change ΔG⁰ increased with temperature and the negative ΔH⁰ and ΔS⁰ values indicate the exothermic nature of adsorption and decreased randomness at the adsorbent-solution interface. In aqueous medium, the water molecules surround the hydrophobic host polymeric matrix and this cage effect is responsible for the reduction in entropy of the system. The regeneration of the adsorbent was effective in alkaline medium and the efficacy of the adsorbent was tested for the removal of chromium from tannery waste water.

Keywords:

• Amberlite XAD-4
• chromium
• aliphatic primary amine
• tannery waste water

Acknowledgments

Financial support from the Department of Science and Technology (DST), New Delhi, India (Project No: SR/S1/IC-42-2007) is gratefully acknowledged. Thanks to Central Electrochemical Research Institute, Karaikudi, India, Indian Institute of Science, Bangalore, India, National Chemical Laboratory, Pune, India, Thiagarajar College, Madurai, India and Indian Institute of Technology, Madras, India for their assistance in characterization of the samples with EDX, CP-MAS NMR, SEM, Powder-XRD, FT-IR and surface area studies.